1. Field of the Invention
The present invention relates to a process for treating the outer-inner surfaces of a porous non-conductor or an electrically-non-conductive porous article, and a modified porous non-conductor or a modified electrically-non-conductive porous article. According to the present invention, for example, hydrophilic, hydrophobic or adhesive properties may be imparted to the outer-inner surfaces of a porous non-conductor, such properties may be enhanced, or a roughening of the outer-inner surfaces of a porous non-conductor may be obtained.
2. Description of the Related Art
Hitherto, for example, an alternating current (AC) or direct current (DC) corona discharge, or a low-pressure or atmospheric-pressure glow discharge has been used, when treating a surface of a porous or non-porous non-conductive material with an electric discharge.
In a process using an AC corona discharge, an article to be treated is brought into contact with a surface of a dielectric layer disposed on a counter electrode or an inducing electrode, such as a plane electrode. A discharge electrode, such as a wire or needle electrode, is spaced apart from the article to be treated at a predetermined interval, generally about 1 mm to several millimeters. Then, an AC high-voltage is applied between the discharge electrode and the counter electrode, in air or an other gas, whereby the surface of the article is treated with a linear corona emitted from the discharge electrode. A dielectric layer is generally disposed between the counter electrode and the article to be treated, to stabilize the emitted linear corona. A suitable gas may be selected in accordance with the functional groups to be introduced to the surface of the article. The surface of the article may be also treated, using a DC corona discharge caused by applying a DC high-voltage instead of the AC high-voltage.
In the above process, more than a certain degree of an electric intensity between the discharge electrode and the counter electrode must be produced, namely, a high-voltage sufficient to initiate the corona discharge, to generate the corona discharge. If the voltage applied is too high, however, a spark discharge between the electrodes may occur through weak portions of the article to be treated, to thereby damage the article, for example, by producing large holes therein. When an article having a rugged or rough surface is treated, a uniform discharge cannot be obtained, and therefore, a uniform treatment of the surface is not obtained, and the article may be damaged, for example, by the producing of holes therein. Further, the gas used has a considerable affect on the stability of the discharge. Some gases cannot generate a stable discharge, and thus, the required treatment may not be obtained.
In a process using a low-pressure glow discharge, a pair of electrodes are positioned separate from and opposite to each other in a discharge chamber in which a vaccum has been obtained. The article to be treated is located between the electrodes, and then the pressure of air or other gas in the chamber is reduced to about 10.sup.-2 Torr to about 10 Torr. An AC voltage of generally several kilohertzs (KHz) to several megahertzs (MHz) is applied between the electrodes, to generate a glow discharge, and the surface of the article is treated therewith. In this process, the AC voltage is applied while the article is not in contact with the electrodes or is in contact with only one of the electrodes. Further, intervals between the electrodes will facilitate the discharge under a reduced pressure, as apparent from Paschen's law, and thus the electrodes can be positioned farther apart than those used in the above process using the AC corona discharge. Under a reduced pressure, very little inactivation of ionized chemical species occurs, with a corresponding reduction of the spark discharge. Therefore, more gases may be used, in comparison with the above process using the AC corona discharge.
The process requires a vaccum apparatus to reduce the pressure in the discharge chamber, and thus is not suitable for a continuous treatment. When an article containing volatile materials, such as water or a plasticizing agent, is treated, it is difficult to control the pressure to one suitable therefor. Further, when a porous article is treated using the low-pressure glow discharge, a discharge cannot occur in small pores, such as pores having a pore size of less than 0.1 mm, in the presence of some gases or under some degrees of reduced pressure, in accordance with Paschen's law. Therefore, an article having surfaces with such small pores cannot be treated.
In a process using an atmospheric-pressure glow discharge, as disclosed in, for example, Kogyo-Kanetsu (Engineering Heating), Vol. 27, No. 1, 1990, a pair of electrodes are positioned separate from and opposite to each other at a predetermined distance (generally, several millimeters) in a discharge chamber which may be sealed. An AC voltage of several kilohertzs (KHz) to several tens of megahertzs (MHz) is applied between the electrodes, while a gas mixture containing one or more rare gases, particularly helium, as a main component, with one or more predetermined reactive gases used to introduce one or more functional groups, is supplied into the discharge chamber. The surface of the article is treated by the glow discharge generated between the electrodes. In this process, a dielectric layer is generally disposed on at least one of the electrodes, to stabilize the generated discharge. Further, the AC voltage is applied while the article is not in contact with the electrodes and/or the dielectric layers, or is in contact with only one of the electrodes and/or the dielectric layers.
This process requires an expensive rare gas to produce a stable generation of the discharge. When the amount of the reactive gases used to introduce the functional groups is increased, the discharge becomes unstable, and thus, the amount of the gases that can be used is limited. The gas mixture may generally contain up to about 10% of the reactive gases. In this process, the discharge occurs only at the portion where the gas flows. When a porous article is treated, the reactive gases cannot easily enter voids in the article. Therefore, it is difficult to treat the surfaces of such voids, and thus it is difficult to uniformly treat the outer-inner surfaces of porous article.
Japanese Unexamined Patent Publication (Kokai) No. 4-74525 discloses a process for a treatment using an atmospheric-pressure glow discharge wherein each of the electrodes located opposite to each other is covered with a dielectric layer. In the process disclosed in Kokai No. 4-74525, an AC voltage is applied while the article is not in contact with the electrodes and/or the dielectric layers, or is in contact with only one of the electrodes and/or the dielectric layers. The above-mentioned Publication does not disclose a process wherein an AC voltage is applied while the article is in direct contact with each of the dielectric layers. Further, the process disclosed in Kokai No. 4-74525 is not operative in air but requires the use of an expensive rare gas as a gas for a stable generating of the discharge.
In the process using the atmospheric-pressure glow discharge, the discharge occurs at the portion where the reactive gas flows. Therefore, it is difficult to uniformly treat the outer-inner surfaces of porous article containing voids, because a treating of the surfaces of voids where the reactive gases do not easily enter is difficult to obtain.
Japanese Unexamined Patent Publication (Kokai) No. 7-119021 discloses an apparatus for a discharge treatment using the atmospheric-pressure glow discharge wherein a pair of cylindrical electrodes covered with a ceramic layer (thickness=0.5 to 2 mm) are disposed in parallel. This apparatus requires an expensive rare gas, more particularly, an atmospheric gas containing mainly a gas mixture of helium and argon. In view of obtaining a stable discharge, the gases which may be used to generate a stable discharge are limited, and the concentration of oxygen is preferably 0.5% or less. The apparatus is not operative in air. Further, the apparatus can treat only the portion in contact with the reactive gases. Therefore, it is difficult to uniformly treat the outer-inner surfaces of porous article containing voids, because a treatment of the surfaces of voids where the reactive gases do not easily enter is difficult to obtain.